Work during the past several years has indicated that the neuroendocrine control of growth hormone and prolactin secretion most likely involves both releasing and inhibiting factors of hypothalamic origin. As a consequence measurement of pituitary hormone levels in plasma alone is insufficient for determining which of the neuroendocrine control mechanisms are responsible for observed alterations in hormone secretion. Three studies involve a multifaceted investigative effort to 1) develop and refine sensitive and specific bioassays for each of the hypothalamic factors controlling growth hormone and prolactic secretion using an in vivo rat model and an in vitro rat anterior pituitary perifusion system coupled with an immunoprecipitation techniques, 2) search for the presence of releasing and inhibiting factors peripheral venous blood, portal hypophyseal blood of patients undergoing pituitary surgery, and in cerebrospinal fluid of normal subjects and of patients with disorders of growth hormone or prolactin secretion. Pharmacologic agents which affect growth hormone and prolactin secretion by altering neurotransmitter function will be used in an attempt to demonstrate changes in the levels of releasing and inhibiting factors. BIBLIOGRAPHIC REFERENCES: Emerson, C.H., Frohman, L.A., and Szabo, M.: Evidence for crossreacting substances to thyrotropin-releasing hormone in human urine. American Federation for Clinical Research, 1977 Annual Meeting. Szabo, M., Nakawatase, C., Kovathana, N., and Frohman, L.A.: Separation of central nervous system and peripheral effects of 1-dopa on the inhibition of prolactin secretion. Endocrine Society, 1977 Annual Meeting.